Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $93.49   4.304%   $97.5138   $97.51   $97.50   $97.50  
  Purchase #2 $189.61   5.296%   $199.6517   $199.65   $199.65   $199.70  
  Purchase #3 $173.62   10.626%   $192.0689   $192.07   $192.05   $192.10  
  Purchase #4 $81.68   4.783%   $85.5868   $85.59   $85.60   $85.60  
  Purchase #5 $153.88   13.578%   $174.7738   $174.77   $174.75   $174.80  
  Purchase #6 $185.42   4.481%   $193.7287   $193.73   $193.75   $193.70  
  Purchase #7 $47.78   6.565%   $50.9168   $50.92   $50.90   $50.90  
  7 purchase totals = $925.48       $994.2405   $994.24   $994.20   $994.30